CHAPTER X. 

 THE PROPERTIES OF MUSCULAR TISSUE. 



Contractility. The characteristic physiological property 

 of muscular tissue, and that for which it is employed in the 

 Body, is the faculty possessed by its fibres of shortening 

 forcibly under certain circumstances. The direction in which 

 this shortening occurs is always that of the long axis of the 

 fibre in both plain and striped muscles, and it is accompanied 

 by an almost equivalent thickening in other diameters, so that 

 when a muscle contracts it does not shrivel up or diminish 

 its bulk in any appreciable way; it simply changes its form. 

 When a muscle contracts it also becomes harder and more 

 rigid, especially if it has to overcome any resistance. This 

 and the change of form can be well felt by placing the fingers 

 of one hand over the biceps muscle lying in front of the bu- 

 rn erus of the other arm. When the muscle is contracted so 

 as to bend the elbow it can be felt to swell out and harden as 

 it shortens. Every schoolboy knows that when he appeals to 

 another to " feel his muscle " he contracts the latter so as to 

 make it thicker and apparently more massive as well as 

 harder. In statues the prominences on the surface indicating 

 the muscles beneath the skin are made very conspicuous 

 when violent effort is represented, so as to indicate that the 

 muscles are in vigorous action. In a muscular fibre we find 

 no longer the slow, irregular, and indefinite changes of form 

 seen in amoeboid slightly differentiated cells; they are replaced 

 by a precise, rapid and definite change of form. Muscular 

 tissue represents a group of cells in the bodily community 

 which have taken up the one special duty of executing 

 changes of form, and in proportion as these cells have fewer 

 other things to do, they do that one better. This contractility 

 of the muscular fibres may be briefly described as a passage 

 from the state of rest, in which the fibres are long and narrow, 

 into the state of activity, in which they are shorter and thicker: 

 this change is made with considerable force, and thus the mus- 



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